The drop was a result of increasing processing volume, despite rises in imports and output, according to data compiled by Xinhua News Agency.
Gasoline stocks went up during the period as fuel demand retreated after the Spring Festival Holiday. In March, China's exports of gasoline jumped 104.5 percent from the previous month.
Demand for diesel picked up as construction activities accelerated after winter ended. During the period, exports of diesel surged 150.7 percent.
Data from the National Bureau of Statistics showed China's crude oil output came in at 190 million tonnes in 2017, down 4 percent from a year earlier.